This invention relates generally to switching amplifiers and, in particular, to a distortion reduction technique for inductive boost amplifiers.
Inductive boost amplifiers yield high efficiency and reasonably low distortion when driving essentially resistive loads. A representative example of such an amplifier is shown in U.S. Pat. No. 5,610,553 entitled xe2x80x9cSwitching Amplifier with Impedance Transformation Output Stage,xe2x80x9d the teachings of which are incorporated herein by reference.
When driving inductive loads, however, amplifiers of this type tend to produce excessive voltage due to their inability to detect back-EMF from the load. This leads to distortion during times of decreasing output voltage.
Use of negative feedback from the amplifier output gives moderate relief from this distortion, but is complicated by phase lags inherent to output filters required in switching amplifiers. Another feedback source is therefore desirable.
The present invention resides in a distortion reduction technique with particular applicability to inductive boost amplifiers. In contrast to existing arrangements, the invention uses the boost voltage itself, rather than the output voltage(s), as feedback to linearize the output. As such, the boost voltage is not subject to the severe time delay of the output filter, yet is sensitive to the effects of back-EMF from inductive loads, which tend to exist at frequencies well below the cutoff frequency of the output filter.